1. Field of the Invention
The present invention relates to a liquid filling nozzle plate used to fill a container with a liquid.
2. Discussion of the Related Art
Conventionally, liquid filling apparatuses have been developed and used for automatically filling containers with liquids, e.g. milk and juice.
FIG. 10 is a sectional side view schematically showing an essential part of a liquid filling apparatus of the type described above. As shown in the figure, the liquid filling apparatus is arranged as follows: A pipe 61 is connected to the bottom of a liquid tank 60, and two check valves 63 and 65 are installed in the pipe 61. Further, a liquid filling tube 67 is attached to a portion of the pipe 61 below the check valves 63 and 65, while a pipe 69 is connected to a portion of the pipe 61 between the two check valves 63 and 65, and a liquid volumetric discharge machine 71 is attached to the lower end of the pipe 69.
Both the two check valves 63 and 65 are resiliently biased upwardly by respective coil springs 64 and 66 so that a liquid can be led only downwardly.
The liquid volumetric discharge machine 71 has a cylinder 73 and a piston 75 vertically movably received in the cylinder 73. The vertical stroke of the piston 75 is fixed.
A liquid filling nozzle plate 80 is attached to the lower end opening of the liquid filling tube 67.
FIGS. 11(a) and 11(b) show the conventional liquid filling nozzle plate 80. FIG. 11(a) is a plan view, and FIG. 11(b) is a front view. As shown in the figures, the liquid filling nozzle plate 80 is formed from a metallic disk 81 provided with a large number of through-holes 83.
There is another conventional nozzle plate consisting of a sieve plate formed from a wire net. This nozzle plate is constructed of a wire net formed by weaving a plurality of longitudinal and lateral metal wires. In this nozzle plate, through-holes are formed in the gaps between the wires.
Next, the operation of the liquid filling apparatus will be described by using mainly FIG. 10. First, the liquid in the liquid tank 60 fills a part extending from the top of the pipe 61 to the end of the liquid filling tube 67 and a part extending from the top of the pipe 69 to the top of the piston 75.
When the piston 75 is pushed down in the direction of the arrow A, the check valve 63 opens, and the liquid in the liquid tank 60 is introduced into the liquid volumetric discharge machine 71.
Then, when the piston 75 is pushed up in the direction of the arrow B, the check valve 63 is closed, while the check valve 65 opens. Consequently, the liquid in the liquid volumetric discharge machine 71 is passed through the liquid filling tube 67 and discharged from the through-holes 83 of the liquid filling nozzle plate 80, thereby being supplied into a container (not shown).
The liquid filling nozzle plate 80 is provided to prevent the liquid filling the liquid filling tube 67 from flowing out (so-called dripping) when no liquid is desired to discharge from the liquid filling nozzle plate 80.
More specifically, the surface tension of the liquid filling the liquid filling tube 67 acts in the large number of through-holes 83 provided in the liquid filling nozzle plate 80, thereby preventing the liquid from flowing out by gravity. Thus, dripping of liquid is prevented.
However, the through-holes 83 provided in the conventional liquid filling nozzle plate 80 are so shaped that, as shown in the sectional view of FIG. 12, the inner surfaces 85 of the through-holes 83 extend straight in the vertical direction.
Therefore, the surface tension acting in the through-holes 83 is not satisfactorily high, so that dripping of liquid is likely to occur. To increase the surface tension in order to prevent dripping of liquid, the diameters of the through-holes 83 may be reduced. However, if the diameters of the through-holes 83 are reduced, the fluid resistance occurring when the liquid is discharged increases undesirably.
In contrast, the wire-net sieve plate provides relatively large surface tension owing to the complicated surface configuration of the openings and is therefore capable of effectively preventing dripping of liquid. With the wire-net sieve plate, however, solid matters in the filling liquid, e.g. fibers and fruit flesh, may be entangled or caught in the intersections of the wires, causing the sieve plate to be clogged. Moreover, because the sieve plate is a wire net, the mechanical strength is low.
In view of the above-described circumstances, an object of the present invention is to provide a liquid filling nozzle plate capable of effectively preventing dripping of liquid without the need to reduce the diameters of through-holes.
Another object of the present invention is to provide a liquid filling nozzle plate capable of effectively preventing dripping of liquid without causing the holes to be clogged with solid matter in the filling liquid.
Still another object of the present invention is to provide a liquid filling nozzle plate having high mechanical strength.